1. Technology Field
The present invention generally relates to optical transmitters. In particular, the present invention relates to an optical transmitter capable of measuring and compensating for the modulation current of a laser included in the transmitter such that an optical signal having sufficient optical characteristics is produced.
2. The Related Technology
A properly operating light source is integral to functionality of an optical transmitter. Such light sources, including a laser diode positioned in a transmitter optical subassembly of an optical transceiver module for example, should conform to pre-defined parameters propounded by the manufacturer or applicable industry. These pre-defined parameters involve various characteristics of the optical signal produced by the laser, such as average light level, extinction ratio (“ER”), and optical modulation amplitude (“OMA”). These parameters, which indicate whether the optical signal is adequate for data transmission purposes, are defined by the particular physical transmissive interface, i.e., Fibre Channel, gigabit Ethernet, Sonet, etc.
Various factors can affect the operating parameters of a laser diode during its optical transmission activities, which can correspondingly cause the laser to exceed acceptable ranges for such parameters. One of these factors is modulation current. As is known, the modulation current of the laser diode within an optical transmitter can affect the above-referenced parameters, i.e., average light level, extinction ratio, and optical modulation amplitude. Should any of these parameters exceed predefined acceptable ranges, the optical signal produced by the laser can be adversely affected.
Previously known transceiver designs have typically not enabled the measurement and/or reporting of laser modulation current data, either internally within the transceiver or to an external host with which the transceiver is operably connected. As a result, transceiver operating parameters can be adversely affected by a modulation current that may be out of specification while the transceiver is in use.
Further, the lack of information regarding laser modulation current can result in more lengthy testing processes to be performed at the time of transceiver assembly. In particular, each laser and/or transceiver must typically be tested and adjusted during assembly to ensure that the above and other operating parameters are maintained within specification during laser operation. To the extent that measurement and adjustment for the modulation current is not performed, the process for laser testing is lengthened due to the fact that other, more time consuming procedures must be performed to ensure adequate laser functionality.
Another factor affecting laser functionality relates to the fact that laser operating properties change over the operational lifetime of the laser. Thus, with all other conditions remaining equal, a laser may still fall outside of acceptable parameter ranges as it advances through its operational lifetime. This operational variability over the life of the laser represents another challenge for maintaining the laser modulation current within proper operational parameter ranges.
In light of the above, a need therefore exists for the determination of modulation current associated with the operation of a laser or other light source disposed within an optical transmitter, such as an optical transceiver module. Moreover, a need exists for the ability to adjust for laser modulation current so as to optimize its operation within the transceiver. Any proposed solution to the above should enable determination and/or adjustment of laser modulation current at time of transceiver assembly and/or during in-field transceiver use.